Corncobs and ‘goats’ could help renewable jets take flight

The jets of the future could be powered by corncobs and wood chips, as scientists hunt for renewable sources of fuel for the aviation industry.

University of Delaware scientists have developed new catalysts which help transform these unlikely sources – known aslignocellulosic biomass - into fuel.

Current sources of renewable jet fuel such as oil and grease or algae require high pressures, and temperatures of around 350°C. The new catalysts the team have developed – known as ‘chemical goats’ – kick-start the chemical reaction that turns the plant material into fuel, both speeding it up and lowering the temperature required.

One of the catalysts is made from inexpensive graphene, looking like a honeycomb of carbon molecules. Its unique surface properties increase the speed of the coupling reaction, and means the reaction can take place at only 60°C.

Another catalyst removes oxygen from the catalyst in an energy-efficient way, and produces high yields of branched molecules – up to 99% - which makes it suitable for high-energy jet fuel. Both catalysts are recyclable, and the processes are scalable.

“The low temperature and high selectivity of our process can enable cost-competitive and sustainable production of bio-based aviation fuels from lignocellulosic biomass,’ said Basudeb Saha, associate director of University of Delaware’s Catalysis Center for Energy Innovation, which is supported by the U.S. Department of Energy.

He said the research’s “very low” catalyst activity – with a 20-hour reaction time and very high catalyst loading – “is not commercially viable, so this is a research challenge that yet remains.”

However, he added: “The technology they have developed seems to achieve good yields, and the target product distribution resembles the mixture from which we currently refine jet fuel.

According to Saha, the two catalysts his team has developed solve two of the biggest hurdles to making renewable jet fuel – coupling and deoxygenation. Once the corncob or wood chip plant material is broken down from a solid to a liquid, it has a low carbon content. So to create the high-carbon, high energy molecules needed for jet fuel, the carbon molecules have to be ‘coupled’ or chemically stitched together.

Then the oxygen from these plant-derived molecules needs to be removed, forming branched hydrocarbons consisting of hydrogen and carbon alone. This is essential to improving the flow of the fuel at the freezing temperatures encountered during high-altitude commercial flight.

“International planes may fly at an altitude of 35,000 feet, where the outside temperature could be as low as -14° Centigrade,” explains Saha, who is leading the renewable jet fuel project at the center. “That's the temperature at which a plane has to run, and the fuel can't be frozen.”

Hallett said the technology had a “noble” end goal. “Bio jet fuel offers the most attractive market for increasing renewable fuels in the transport sector, as it is highly regulated and it is an industry with fuel surcharges already built into travel costs, and with fewer, higher volume customers the market penetration seems easier,” he said.

The research is detailed in two articles published in ACS Catalysis, and one in ChemSusChem.

Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.